Experimental investigation of multistage electrodialysis for seawater desalination

Electrodialysis (ED) is currently used for selective removal of ions and brackish water desalination, while for seawater desalination ED is considered to be too energy intensive. This research focuses on the viability of ED using multiple stages for seawater desalination. With staging, the driving force is adapted to the governing conditions at that specific stage, operating at its individual optimum at lower energy consumption. An ED multistage configuration is examined that contains up to four stages. We compare single stage with multistage ED and investigate the effect of operation parameters. Different current densities are applied and optimized and residence time is compared to describe both transmembrane salt and water fluxes. We showed that desalination from 500 mM to 200 mM is possible, but that for these desalination conditions a multistage and single-stage system perform equal. Operation of each stage of the multistage close to limiting current density shows that desalination of synthetic seawater close to drinking water quality is possible. To reach this, the energy consumption is 3.6 kWh/m3 and at least 4 stages are needed. Although outlet concentrations between ED and RO are different, this non-optimized ED system showed double the energy consumption of the state-of-the-art desalination technology RO.